The most common example of echolocation is in Bats, who emit ultrasonic noise and listen for its return (echo) to judge the location of objects. [Kripthor] doesn’t need to generate the sound himself, he just needs to pick it up at different points. The time difference from the three samples can be used to triangulate coordinates as seen in the image above.

He first tried using a PC sound card to collect the samples. The stereo input only provides two channels so he tinkered around with a 555-based multiplexing circuit to sample from three. The circuit noise created was just too great so he transitioned to using an Arduino. The ADC samples from each microphone via an NPN transistor which is used as a simple amplifier.

[Tony Messina] had been fascinated with bat’s echolocation since he was a kid. After he retired, he decided to act on this fascination and built a simple bat detector.

The simple bat detector uses frequency division to lower the bat’s chirping to a frequency we can hear. For example, if a bat is calling at 91kHz the system will divide it by 16 and put out 5.7kHz. The system is digital, so all amplitude is lost. You’ll just hear clicks like a Geiger counter. Being digital has its advantages though. Unlike similar analog devices that have to be tuned to a small frequency range, the simple bat detector can detect a much wider window.